Recently, with increasing demand for small, high power light emitting elements, there is increasing need for a large flip chip type light emitting element having good heat dissipation efficiency. A flip chip type light emitting element includes an electrode directly bonded to a secondary substrate and does not employ a wire for supplying external power to the flip chip type light emitting element, thereby providing much better heat dissipation efficiency than a horizontal light emitting element. Therefore, the flip chip type light emitting element allows effective heat transfer towards the secondary substrate upon application of high density current thereto and thus can be suitably used as a high power light source.
Furthermore, in order to achieve size reduction and high output of a light emitting element, there is increasing need for a chip scale package that uses a light emitting element as a package by omitting a process of packaging the light emitting element in a separate housing. Particularly, since the electrode of the flip chip type light emitting element can act as a lead of the package, the flip chip type emitting device can be advantageously applied to such a chip scale package.
A chip scale package structure is more vulnerable to heat generated during high current driving. Thus, in order to improve reliability of a light emitting element through efficient heat dissipation, an external electrode such as a metal bulk is used and a certain region of the light emitting element must be secured by the external electrode.
On the other hand, the light emitting element emits light upon receiving power through an electrode electrically connected to a semiconductor layer. If a contact region between the semiconductor layer and the electrode is not sufficient and is present only in a certain region of the light emitting element, the light emitting element allows strong light emission at a certain location of the semiconductor layer due to insufficient spreading of electric current applied from an external power source. Specifically, since electric current flows to the semiconductor layer only through a certain contact region between the semiconductor layer and the electrode when supplied through the metal bulk, light emission is not efficiently performed in other regions of the semiconductor layer at which the electrode does not contact the semiconductor layer. Therefore, the light emitting element suffers from deterioration in luminous efficacy.
Generally, when a substrate is removed from the light emitting element, stress and strain occur on the light emitting element. The stress and strain are transferred to a light emitting structure, generating cracks in the light emitting structure. To solve this problem, although a thick metal pad or a polymer such as EMC is disposed under the light emitting structure, this structure also has a problem in that cracks are generated mainly at the center of the light emitting structure near an upper side of the polymer.
Therefore, there is a need for a light emitting element that can secure efficient heat dissipation and has good mechanical properties and improved current spreading efficiency.